Purpose of hood insulation pad

tgross

Member
My 2004 Sprinter 2500 is missing the hood insulation pad. Before I get a replacement, I wanted to know what its purpose is. Is it for sound, thermal, both, something else? Please share your thoughts.
 

irvingj

2015 RT SS Agile (3.0L)
My thoughts: As far as I know, all diesels --"soft" diesels, at least; no experience with OTR trucks-- have them. I believe mostly for sound attenuation, though in cold weather operation they help with thermal retention as well. My '82 Peugeot 504D Estate, my 2005 Jetta TDI Wagon, and our Sprinter all had/have heavy under-hood & firewall insulation.
 

MTGJR1

Well-known member
I believe every auto I have ever owned has good insulation. Pretty sure it provides thermal protection to good and noise absorption. Experiment to show what it does to reduce sound level: put a buzzer type doorbell in a coffee can and activate. Now line the coffee can with absorbing foam and activate the buzzer. Can only actually amplifies sound.
 

BrennWagon

He’s just this guy, you know?
My understanding is that the hood insulation is there as a fire blanket in case of an engine fire, thermal and sound insulation are secondary
 

220629

Well-known member
My understanding is that the hood insulation is there as a fire blanket in case of an engine fire, thermal and sound insulation are secondary
I've heard that also, but don't know if it is true. There is no reason to protect the metal hood aka bonnet from the fire. It won't burn. One theory I heard is that the insulation falls down to smother the fire. The insulation falling down, assuming that it even will release and fall, given the engine compartment shape/design of a Sprinter I doubt it will fit tight enough to block oxygen and smother a fire.

FWIW. I lean toward sound and perhaps thermal issues.

:2cents: vic
 

elemental

Wherever you go, there you are.
I lean towards sound attenuation as the primary purpose. I believe diesel IC is louder in the engine compartment than gasoline IC, so sound attenuation under the hood is even more critical. I remember researching "alternatives" to gasoline IC in the 1980s, and diesel was being promoted but with the caveat that it required more sound attenuation to make it acceptable to consumers.

Here is a Reddit discussion (if you want to get an Internet expert opinion): https://www.reddit.com/r/explainlikeimfive/comments/6k859b and this ResearchGate: https://www.researchgate.net/post/Why_do_diesel_engines_produce_more_noise_than_petrol_engines
 

tgross

Member
Thanks all! You gave me 3 good reasons to purchase a new pad. I don't know the order of importance of the 3, but for $70, I don't need to over-think it.
 

irvingj

2015 RT SS Agile (3.0L)
Ha-ha.. absolutely! Forgot about "#4"!!

Due to parking outside, both my Peugeot and my VW have had -- in the past -- infestations of mice. They went other places too, but in both cases they went for the under-hood insulation. Tough call; there's a thread on this forum about ridding our vehicles of creatures -- give it a read. To get rid of them? It can be easy... or it can be hard.

Keep my VW in a garage now, so no further issues, and --so far-- our Sprinter has only had paper wasps move in to voids around the front doors while it's been parked outside for extended periods. (My 504D died some years ago...)
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the dude

Member
Maybe the hood insulation is the reason for my " black " hood to be repainted now ,,,,, 6 times . 2014 -144 WB -I-4 . The MB specified paint shop said , " this maybe an annual repaint " . MB & the paint supplier are paying .
 
A layer of bedliner on the topside of the engine hood also acts as a great sound deadener besides the never rust again, never have any rock damage again factor.

Diesels deserve to be muffled in any way we can and with the lackluster MB paint jobs on these 'work vehicles' which is no excuse, sealing the paint is recommended in any way we can.

Keeping mice from setting up shop in the padded insulation takes its own precautions like fragrant dryer sheets, ultrasonic sound units, not so sure about this one, hot pepper, capsacian impregnated electrical type of tape available at Honda dealers or online, lights at night in the engine compartment.

Many have tried many things to repel rodents and the damage they can do. To protect wiring specifically, the hot pepper tape works. It would be fun to see a video of a mouse first trying to chew through this tape. If this could be applied to the padded insulation somehow it could work there too. Maybe underneath the insulation?
 

Allobet

Member
Can you send the specs of the padded part under the hood? I had mice chew on it and bring it into the house and built cozy nests between the stove fan and the top shelves that I only discovered after 15A fuse blew up.
I sprayed the hell of this pad with peppermint rodent repellent. Can’t put the van in pitched roof garage... time for a new home that allows the 11ft beast to fit in??
 

Attachments

powderhound

Member
….
4. Provides a home for mice and small birds
5. Protects the paint/clear coat from excessive heating and rapid cooling…maybe?

About #4…

2004 Sprinter. 310k miles. Stored in the winter. Lots of dryer sheets, steel wool, minty scents..stored in Northern New Hampshire one cold, cold winter. Modern Morton Building with a concrete floor. I knew the mice had some relative warmth that year, as it was clear someone had harvested some insulation from the firewall pad on the passenger side. Upset me given my thoughtful mitigation before storage. Aw well, it was cold!!!!

Welp, a number of years later now and I have at least half the mojave’s sand in the hood liner. And that is only what remained after 10 years of XC driving. Finally ordered replacment hood and vent insulation. Removed the original pad this afternoon. Low and behold, I find my firewall insulation nested between the pad and the hood. Place was dark and warm…that’s for sure!!

Took a bit of cleaning the underside of the hood. And, yup, I’ll be treating some mind-boggling rust patches before installing the new pad. If only I could figure out what tool I need/don’t need to remove the original retention clips without damaging the metal ?

Hood Insulation Pad-SPRINTER 2002-2006
901 831 00 96

Hood Insulation Pad Mounting Plug-SPRINTER 2002-2006
123 990 02 92 (12 needed, order extra)

Cabin Filter Insulation Kit 2002-2006
909 835 04 00 05 00
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E6FA67AA-C300-42DF-8BFB-CF173384B766.jpeg
 
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Maybe some hot pepper flakes could be added to the insulation pad. Or an infused hot pepper sprayable liquid applied all over and under the pad. Peppermint oil, with regular respraying could work too. I prefer the hot pepper route, flakes, tape, whatever form that can be applied to all the sides of the engine pad. I tried a few mouse traps loaded with peanut butter in the engine compartment and got nada. Must mean, I don't have any rodents. If only....
 

Pickleball

2022 2500 144 High roof 4 cyl diesel
our Sprinter has only had paper wasps move in to voids around the front doors while it's been parked outside for extended periods.
Had wasps or hornets or something plug up A/C drain tube on a Prius with mud which resulted in condensate running into floor of foot rest area.
 

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